This invention relates generally to capacitors, and, more particularly, to capacitors having an extremely low inductance.
Low-inductance capacitors are particularly useful in applications requiring rapid current discharges. An example of such an application is an exploding bridgewire or exploding foil initiator system, where an electrical charge stored on a capacitor is discharged through a bridgewire or foil to vaporize it and thereby accelerate a mass toward an explosive pellet. The resulting impact creates a shock wave in the pellet that brings about an explosion. Another application for such a capacitor is in a strobe light system where an electrical charge stored on the capacitor is discharged through a gas discharge tube, to provide a flash of light. In all of such applications, the capacitor preferably has as low an inductance as possible, so as to maximize the instantaneous current.
Low-inductance capacitors are frequently formed by interleaving and winding together two elongated foil strips with two elongated dielectric strips, to form a cylindrical roll. The foil strips have substantially the same width, but are offset laterally with respect to each other such that their side edges define spiral-shaped projections at opposite ends of the roll. Leads are attached to the two spiral projections by soldering a pair of metal disks or rings against the ends of the roll or by simply axially compressing the disks or rings against the ends. Conductive epoxy terminations are also used.
Although the low-inductance capacitors described above have proven generally satisfactory, they are not believed to be as effective and reliable as is possible. The electrical connections to the two spiral projections, for example, are not believed to be as secure as possible. Additionally, the cylindrical shape of the capacitors is not always preferred. This is especially the case where the capacitor must be attached to a conventional foil strip transmission line, which includes two foil conductors (e.g., copper) secured to the opposite sides of a flat insulator (e.g., Kapton), and which itself has a generally low inductance. In such situations, the capacitor preferably has a flat, rectangular configuration.
It should therefore be appreciated that there is a need for an improved low inductance capacitor of the type formed by interleaving and rolling together two foil strips with two dielectric strips. In particular, there is a need for such a capacitor with an improved means for electrically connecting to the two foil strips, and a need for a capacitor configuration that better lends itself to connection to a conventional foil strip transmission line.